Vatican Secretary of State Cardinal Tarcisio Bertone and the five bishops who investigated the Legion of Christ for the Vatican had been scheduled to meet privately, and the Pope's attendance came as a surprise.
He will be deciding what reforms to mandate for the order -- whether to close the order or install new leadership from outside, as has been rumored.
Vatican spokesman Father Federico Lombardi said the meeting may continue on Saturday.
Father Marciel Maciel, who died in 2008, had been a consummate fundraiser who ingratiated himself with the wealthy Catholics and recruited charismatic priests.
He also maintained close relationships with former Pope John Paul II and other powerful leaders in the Vatican.
The Legion once had an annual budget of more than $600 million, seminaries in two dozen countries, hundreds of priests and 70,000 lay followers.
Pope Benedict, while still Cardinal Ratzinger, had initiated an investigation of sex abuse charges against Maciel, and in 2006, as Pope, he forced Maciel out of the active priesthood, though he did not defrock him.
In a statement issued this March, the Legion of Christ admitted that Maciel had abused seminarians.
Last year, the order issued a statement admitting that its founder had fathered at least one child.
He is accused of fathering children with several women.
The five bishops who are meeting with Pope Benedict today were appointed as Visitors to the Legion, meaning they visited all the centers of the Legion throughout the world as part of an investigation.
They had completed their Visitation and finished their report by the start of April and were called to Rome to meet with the pope and the secretary of state.
SIC: ABC